You may have already figured this out but here goes.
You can use Cisco's VSM quote tool to get the best mix for the space you have. Are you 100% recording or using motion/event recording?
Your media server should be set up to use 95% of the available space. That is to say even if VSOM thinks the storage space is totally full it's really only 95%. I believe that is to keep the VSMS from crashing.
Good luck.